1. Technical Field of the Invention
The present invention relates to a method and an apparatus for controlling electric power generation for vehicles, which control output voltage of a generator loaded on such vehicles as passenger cars and trucks.
2. Related Art
In a state where engine rotation is unstable immediately after starting, electric power generation sharply increases torque load. To prevent this problem, various ideas have been proposed. As an example, a technique is proposed for preventing an engine stall due to the large reduction of generated voltage caused by the increased amount of electrical loads when the electric power generation is restrained. According to the technique, when starting the engine, a function is masked (prohibited) which releases the restraint of the electric power generation when the voltage is below a predetermined value. Next, when detecting the completion of gradual generation control immediately after starting, starting is determined to be completed and the mask of the function is immediately released. Consequently, an engine stall due to the subsequent reduction of voltage is prevented. Such a technique is disclosed, for example, in Japanese Patent Laid-open Publication No. 2006-271096.
In recent years, a vehicle system is known which controls electric power generation by communicating with a vehicle ECU (Electronic Control Unit) to finely control the generation in cooperation with the vehicle ECU. The vehicle system changes regulated voltage in response to a communication signal. In addition, the vehicle system performs control for directly restraining excitation current instead of the conventional control for restraining the electric conductivity of the excitation current.
In the above-described conventional vehicle system, the electric power generation may be stopped by setting the regulated voltage to a voltage lower than the release voltage of the battery during the engine start, or the generation may be restrained by setting the excitation current to a low current. According to the conventional method of determining the completion of the engine start, if lowering the regulated voltage to restrain the electric power generation, an output terminal voltage becomes equal to or higher than the regulated voltage during the engine start. Consequently, the completion of the engine start is determined, and the mask is released in a state where the engine rotation is still practically unstable. If limiting the excitation current to a low current to restrain the electric power generation, gradual generation control is interrupted. Consequently, the completion of the engine start cannot be determined. Although the engine start has been practically completed and the engine is sufficiently stable, the function for releasing the restraint of the electric power generation is left to be masked, until the instruction for restraining the generation is released and the completion of the engine start is determined. Thereby, when a large electric load is applied, the voltage generated by the generator can drop, causing an engine stall.